Semiconductor devices are used in a large number of electronic devices, such as computers, cell phones, and others. Semiconductor devices comprise integrated circuits that are formed on semiconductor wafers by depositing many types of thin films of material over the semiconductor wafers, and patterning the thin films of material to form the integrated circuits. Integrated circuits include field-effect transistors (FETs) such as metal oxide semiconductor (MOS) transistors.
One of the goals of the semiconductor industry is to continue shrinking the size and increasing the speed of individual FETs. To achieve these goals, fin FETs (FinFETs) or multiple gate transistors will be used in sub 32 nm transistor nodes. For example, FinFETs not only improve areal density but also improve gate control of the channel.
In recent years, FinFETs have been constructed with a stressor in order to enhance performance. In some circumstances, the stressor may be formed using silicon germanium (SiGe) grown through a single layer epitaxy process. The stressor may be relaxed using SiGe with a high Ge percentage or by implementing a high temperature anneal process. A gradient Ge percentage of SiGe epitaxy may be used to provide strain.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.